To be fair, some airlines have business class agreements on ZEDs. I don't know about other airlines so much, but on UA we'll upgrade just about any frequent flyer with a hint of status, so our odds of getting an upgrade have plummeted. But it has happened. For example, LAS-DEN tends to be filled with tourists who don't fly much. Put them on a 757 with 24 seats in F on a Saturday morning, and there's a good chance you'll get one of them. I've had a couple (short) flights where I've had F all to myself as a nonrev! But generally, that comes at a price. Even if that price is reasonable. I want to say business ZEDs are roughly double in fare.